The 1080p version is available ready to burn, with menus etc. Not much point creating an ISO for the 4K version, as most people can’t burn it, and those who can probably won’t be able to play it anyway.
If you reduce the bitrate far enough to fit it on a BD50, it may or may not play on your UHD player (most won’t). blank BD 100 M discs are not cheap, and many will not work on your stand alone UHD player.
Most UHD players have a USB input, and can play MKV files, so why not just put that file on an external drive or USB stick and plug that in? Why bother with burning a disc at all? Is it really worth all that extra effort just to see a menu and click play? The end result is exactly the same: you watch the movie on your TV.
If all you want is a case on the shelf, then print one out and stuff an SD card or USB stick inside it.